Coronary artery disease is the single leading cause of human mortality and is annually responsible for over 900,000 deaths in the United States alone. Additionally, over 3 million Americans suffer chest pain (angina pectoris) because of it. Typically, the coronary artery becomes narrowed over time by the build up of fat, cholesterol and blood clots. This narrowing of the artery is called arteriosclerosis; and this condition slows the blood flow to the heart muscle (myocardium) and leads to angina pectoris due to a lack of nutrients and adequate oxygen supply. Sometimes it can also completely stop the blood flow to the heart causing permanent damage to the myocardium, the so-called "heart attack."
The conventional treatment procedures for coronary artery disease vary with the severity of the condition. If the coronary artery disease is mild, it is first treated with diet and exercise. If this first course of treatment is not effective, then the condition is treated with medications. However, even with medications, if chest pain persists (which is usually secondary to development of serious coronary artery disease), the condition is often treated with invasive procedures to improve blood flow to the heart. Currently, there are several types of invasive procedures: (1) Catheterization techniques by which cardiologists use balloon catheters, atherectomy devices or stents to reopen up the blockage of coronary arteries; or (2) Surgical bypass techniques by which surgeons surgically place a graft obtained from a section of artery or vein removed from other parts of the body to bypass the blockage.
Conventionally, before the invasive procedures are begun, coronary artery angiography is usually performed to evaluate the extent and severity of the coronary artery blockages. Cardiologists or radiologists thread a thin catheter through an artery in the leg or arm to engage the coronary arteries. X-ray dye (contrast medium) is then injected into the coronary artery through a portal in the catheter, which makes the coronary arteries visible under X-ray, so that the position and size of the blockages in the coronary arteries can be identified. Each year in U.S.A., more than one million individuals with angina pectoris or heart attack undergo coronary angiographies for evaluation of such coronary artery blockages. Once the blocked arteries are identified, the physician and surgeons then decide upon the best method to treat them.
One of the medically accepted ways to deal with coronary arterial blockage is percutaneous transluminal coronary angioplasty (PTCA). In this procedure, cardiologists thread a balloon catheter into the blocked coronary artery and stretch it by inflating the balloon against the arterial plaques causing vascular blockage. The PTCA procedure immediately improves blood flow in the coronary arteries, relieves angina pectoris, and prevents heart attacks. Approximately 400,000 patients undergo PTCA each year in the U.S. However, when the arterial blockages are severe or widespread, the angioplasty procedure may fail or cannot be performed. In these instances, coronary artery bypass graft (CABG) surgery is then typically performed. In such bypass surgery, surgeons typically harvest healthy blood vessels from another part of the body and use them as vascular grafts to bypass the blocked coronary arteries. Each vascular graft is surgically attached with one of its ends joined to the aorta and the other end joined to the coronary artery. Approximately 500,000 CABG operations are currently performed in the U.S. each year to relieve symptoms and improve survival from heart attack.
It is useful here to understand in depth what a coronary arterial bypass entails and demands both for the patient and for the cardiac surgeon. In a standard coronary bypass operation, the surgeon must first make a foot-long incision in the chest and split the breast bone of the patient. The operation requires the use of a heart-lung machine that keeps the blood circulating while the heart is being stopped and the surgeon places and attaches the bypass grafts. To stop the heart, the coronary arteries also have to be perfused with a cold potassium solution (cardioplegia). In addition, the body temperature of the patient is lowered by cooling the blood as it circulates through the heart-lung machine in order to preserve the heart and other vital organs. Then, as the heart is stopped and a heart-lung machine pumps oxygenated blood through the patient's body, the surgeon makes a tiny opening into the front wall of the target coronary artery with a very fine knife (arteriotomy); takes a previously excised saphenous vein (a vein from a leg) or an internal mammary artery (an artery from the chest); and sews the previously excised blood vessel to the coronary artery.
The most common blood vessel harvested for use as a graft is the greater (long) saphenous vein, which is a long straight vein running from just inside the ankle bone to the groin. The greater saphenous vein provides a bypass conduit of the most desired size, shape, and length for use with coronary arteries. The other blood vessel frequently used as a bypass graft is the left or right internal mammary artery, which comes off the subclavian artery and runs alongside the undersurface of the breastbone (sternum). Typically, the internal mammary artery remains attached to the subclavian artery proximally (its upper part) but is freed up distally (its lower part); and it is then anastomosed to the coronary artery. However, the saphenous vein graft should be sewn not only to coronary artery but also to the aorta, since the excised vein is detached at both ends. Then, to create the anastomosis at the aorta, the ascending thoracic aorta is first partially clamped using a curved vascular clamp to occlude the proper segment of the ascending aorta; and a hole is then created through the front wall of the aorta to anchor the vein graft with sutures. The graft bypasses the blockage in the coronary artery and restores adequate blood flow to the heart. After completion of the grafting, the patient is taken off of the heart-lung machine and the patient's heart starts beating again. Most of the patients can leave the hospital in about 6 days after the CABG procedure.
It will be noted that coronary artery bypass surgery is considered a more definitive method for treating coronary arterial disease because all kinds of obstructions cannot be treated by angioplasty, and because a recurrence of blockages in the coronary arteries even after angioplasty is not unusual. Also coronary artery bypass surgery usually provides for a longer patency of the grafts and the bypassed coronary arteries in comparison with the results of PTCA procedure. However, coronary artery bypass surgery is a far more complicated procedure, having need of a heart-lung machine and a stoppage of the heart. Also, it is clearly the more invasive procedure and is more expensive as a graft to the coronary arteries such as the left anterior descending, diagonal branches, and ramus intermedius arteries (which are located on the surface of the heart relatively close to the left internal mammary artery). However, there are several disadvantages associated with a CABG operation with a left internal mammary artery graft, which are as follows: (1) technically, this artery is more tedious to take down; (2) sometimes the left internal mammary artery is inadequate in size and length; (3) the operation is suitable only for the five percent of candidates for coronary artery bypass because only a single left internal mammary artery is available as a graft; (4) anatomically, the operation is limited mainly to the left anterior descending coronary artery because of its location ad length; and (5) the majority of patients need more than single vessel bypass surgery.
In comparison, coronary arteries as small as 1 mm in diameter can be revascularized by vein grafting; and the saphenous vein is longer, larger, and more accessible than the left internal mammary artery. Equally important, although the greater or lesser saphenous veins of the leg are preferred, the cephalic or basilic veins in the arm are available as alternatives when the leg veins in the patient are unavailable or are unsuitable. For these reasons, the vein graft has today become the standard conduit for myocardial revascularization.
There remains, however, a long-standing and continuing need for a bypass technique which would allow surgeons to perform multiple bypass procedures using vein grafts as vascular shunts in a minimally invasive way, and, in particular, the need remains for a simpler method to place more than one vein graft proximally to the aorta and distally to the coronary artery without using a heart-lung machine and without stopping the heart. If such a technique were to be created, it would be recognized as a major advance in bypass surgery and be of substantial benefit and advantage for the patient suffering from coronary artery disease.